The invention relates to alternate fuels for the transportation industry and, in particular, relates to a system for utilizing natural gas as a fuel for road vehicles.
Natural gas offers an alternative fuel for road vehicles and is currently used as such on a limited scale. In most instances, in current use, natural gas is carried aboard the vehicle in a high-pressure tank with a working pressure of, for example, 3,000 or 3,600 psi. Conventionally, the vehicle fuel tank is filled from a battery of tanks storing gas at a pressure somewhat higher than the vehicle tank working pressure or is filled over a relatively long period, overnight for example, from a small compressor.
These conventional tank filling systems are not well-suited for use with those large transportation vehicles which must be refueled in a relatively short time, for example, of several minutes to satisfy established operational constraints related to servicing, storage and/or usage procedures. The capital cost of a bank of storage tanks or of a compressor that can deliver flow rates to satisfy a fast-fill requirement can be prohibitive. Further, a refueling depot for mass transit busses, highway trucks, or other high fuel volume applications may exist at a location not served by a natural gas pipeline or by a pipeline of adequate capacity. Liquid natural gas (LNG) offers relatively high energy per unit volume and could be readily employed in a relatively inexpensive refueling facility for fast-filling of large transportation vehicles. However, in some locations LNG cannot be carried on-board in a vehicle fuel tank because of safety regulations.